Two recommended books:
Everything*You*Know About CSS*Is*Wrong! - SitePoint Books
HTML*Utopia: Designing*Without*Tables Using*CSS, 2nd*Edition - SitePoint Books
Generally use tables for tabular data. Use CSS / XSLT for styling.
Different style sheets can be used to make:
- Your site more accessible.
- Easier to adapt to mobile devices.
- Easier to modify your site wide styling in central single style sheets.
- That also means that the site will load faster since the style sheet is already in the servers primary storage / memory.
I doubt any
direct
SEO effect.